US2726933A

US2726933A - Production and use of sulfur dioxide

Info

Publication number: US2726933A
Application number: US265644A
Authority: US
Inventors: Henry F Merriam; Howard H Hurmence
Original assignee: Allied Chemical and Dye Corp
Current assignee: Allied Corp
Priority date: 1952-01-09
Filing date: 1952-01-09
Publication date: 1955-12-13
Anticipated expiration: 1972-12-13

Description

Dec. 13, 1955 H. F. MERRIAM EVAL PRODUCTION AND USE OF SULFUR DIOXDE 2 Sheets-Sheet l Filed Jan. 9, 1952 bm mmmzzou 353m Nm.

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MHSOJ@ mdmIamOhQ OP INVENTORS. HENRY F. MERRIAM HOWARD H HURMENCE BY Lgf P0@ ATTORNEY.

United States Patent O PRODUCTION AND USE F SULFUR DIOXIDE Henry F. Merriam and Howard H. Hurmence, West Orange, N. J., assignors to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of N ew York Application January 9, 1952, Serial No. 265,644

6 Claims. (Cl. 23-179) The present invention relates to process for combustion of elemental sulfur to produce high quality sulfur dioxide free or reasonably so of sulfur and oxygen. According to certain aspects of the invention, sulfur dioxide produced is used under controlled conditions to oxidize gaseous sullides to form recoverable elemental sulfur and the elemental sulfur employed in the aforementioned process.

Production of sulfur dioxide containing little or no free oxygen and sulfur has inthe past presented substantial design and operational diiculties. Relative freedom from both these substituents has been realizable by space combustion at high ame temperature, typically of the order of 2800o F., within large volume combustion zones when employing precisely controlled ratios of sulfur and oxygen. Removal of combustion heat, control of furnace wall temperatures, and cooling of hot combustion gases have dictated adoption of extensive auxiliary plant including waste heat boilers and other cooling circuits representing substantial operating and Ymaintenance as well as investment costs.

On the other hand, combustion of liquidsulfur effected Within a body of the same has resulted in a stream of gaseous product heavily laden with vaporized elemental sulfur which is undesirable for certain uses to which sulfur dioxide is well adapted. Also, such sulfur tends to deposit as liquid or as solid upon surfaces of equipment, creating or aggravating operational and design difficulties.

Among objects of the present invention is production of high quality sulfur dioxide which does not tend to form sulfur deposits, and which contains otherwise acceptably low quantities of sulfur, even substantially none, as well as being substantially free of oxygen.

The invention has for further objects such other improvements and such other operative advantages or results as may be found to obtain in the process or apparatus hereinafter described or claimed.

In accordance with the invention, oxygen supplied in a stream of gas is brought into contact with liquid sulfur maintained at auto-ignition temperature within a reaction zone comprising a pool of that material. Resultant gases comprising sulfur dioxide are contacted further with liquid sulfur having temperature below auto-ignition level for time and at other conditions adequate to substantially reduce the temperature of those gases. It has been found in practice of the invention that there is produced sulfur dioxide containing desired low quantities of free sulfur and free oxygen down to practical freedom from both, in concentrations consistent with the concentration of oxygen in the stream of gas reacted with the liquid sulfur, e. g. of the order of about 20-2l% when that gas is air.

In preferred operation, the oxygen-laden gaseous material is introduced to a combustion zone within a relaitvely deep pool of liquid sulfur sufficiently below its top surface, for example, at or adjacent the bottom of the pool, that all or substantially all of the oxygen is consumed during passage of the gas toward that surface.

ICC

Hot liquid sulfur continuously withdrawn from the pool at auto-ignition temperature is cooled in an external cooling zone to substantially below such temperature and returned to the pool, at such circulation rate as to remove heat of combustion of the sulfur burned and additionally to cool sulfur dioxide-containing product to desired extent, even to below minimum auto-ignition temperature of sulfur, if desired. The cooled liquid sulfur may be intimately contacted with product gases during its movement toward the combustion zone, as prior to admission to the pool, thereafter, or both. Resultant cooled gas is substantially free of oxygen and contains substantially reduced quantities of free sulfur. If the gases are cooled by the process of the invention to temperatures below minimum auto-ignition temperature, by say about 200 F. or more, then their Sulfur content may be nil for practical purposes; they may be used without further puritication for bleaching or other reaction processes wherein substantially sulfur-free sulfur dioxide is desired or required.

For eiciency and economy of operation it is highly desirable that the recirculation of the liquid sulfur to and from the pool be at such rate that average auto-ignition temperatures obtaining within the pool are below 700 F., preferably in the range of about 550-650 F. Higher temperatures of product gases issuing from the pool would be obtained if liquid sulfur were not recirculated through the pool and external cooling zone in accordance with preferred aspects of the invention. At such higher temperatures, which may occur within localized portion of the pool, as adjacent inlets for oxygen-containing gas, the product gases contain substantially larger quantities of elemental sulfur resulting from vaporization of sulfur content of the pool. In practice of the invention, by recirculation of liquid sulfur through the external cooling zone and thence into contact with sulfur dioxide-containing product, including within the pool, elemental sulfur content of such gases may be kept at relatively low values consistent with economical and other advantageous processing of such gases.

To achieve the desired control of combustion and character of the combustion product, it is preferred that the air or other oxygen-bearing gas employed be admitted to the sulfur pool adjacent its bottom as a plurality of spaced thin streams, as may be obtained, for example, by use of manifolded small oritices or of serrated bubble caps. Such admission facilitates complete consumption of oxygen in such gas and production of product of desirably low content in free sulfur.

For advantageous operation, it is preferred that at least part of the liquid sulfur withdrawn from the combustion zone be cooled to temperature Within the lower of the temperature ranges in which it has low Viscosity, e. g. to about 250 3l0 F., and, at such temperature, be sprayed or even atomized into free space above and contiguous to the pool at suitable distance above iiquid level in the latter, to fall countercurrently to and in intimate heat exchange relation with sulfur dioxide-laden gases leaving the pool. ln this manner, etiicient contact and heat exchange between the sulfur and gases and cooling of the latter may be had even during heating of the sulfur through the range of temperatures wherein it is at high viscosity. During a substantial portion, if not all, of the time its temperature is increasing within that range, the liquid is in suspended form; hence its Viscosity has no substantial bearing on electiveness of Contact or heat exchange.

When it is desired that the sulfur dioxide product have very low content of free sulfur and be at low temperature,

` as for example, in supplying sulfur dioxide for bieaehing or reduction of paper or other cellulose material, and for exothermic reaction with hydrogen sulfide to produce conduit 15. The mixture of gases, after owing countercurrent with the liquid sulfur passing downwardly in the condenser, passes via line 23 to heater 29 which serves'to preheat the mixture of gases to desired extent. The mixturel then passes to converter 24 containing a bed of suitable catalyst 25.

When the hydrogen sulfide-containing gas also comprises hydrocarbons, maximum catalyst temperatures are preferably controlled at a level which does not eiect appreciable conversion of hydrocarbons in order to avoid temporary or permanent poisoning of the catalyst by carbonaceous deposits. Many catalysts of the type which promote the oxidation of hydrogen suliide, for example activated bauxite or activated alumina, with or without additional catalytic metal oxides, are known to promote at elevated temperatures hydrocarbon reactions resulting in formation of such deposits. For this reason, and also since low inlet catalyst temperatures tend to favor increased yields, minimum operable inlet catalyst temperatures are preferred and may be realized by cooling the sulfur dioxide product by means of the liquid sulfur scrubbing step described above.

Product gases resulting from the catalytic conversion and containing substantial quantities of sulfur vapors pass through conduit 26 into the bottom of sulfur condenser 27 containing suitable packing 28, such as ceramic bodies, subway grating or angle iron crossbars. The gases ow upwardly in the condenser countercurrent with liquid sulfur maintained at a temperature below auto-ignition level, preferably in the range of about 250-3l0 F., and pumped to the top of the condenser from overflow compartment 37 of sulfur pit 11 through valved line 3S by means of pump 18. Sprays 31 distribute the liquid sulfur downwardly at suiiicient rate to remove sulfur vapors from the upwardly iiowing gases, and the liquid sulfur then passes back to cooling compartment 36 of the sulfur pit through

conduits

32 and 21. Residual gases unremoved by the liquid sulfur in condenser 27 pass out through conduit 33 and are discharged to the atmosphere or collected in a suitable manner if they contain valu'able constituents. lf desired, product sulfur may be withdrawn from the sulfur pit through valved lines 3S and 34 by means of a pump 18.

Referring to Figure 2 in detail, the source of air used in the generation of sulfur dioxide is a blower 5l. Air is passed in valved line 52 through a pool of liquid sulfur maintained at auto-ignition temperature, preferably in the range of about 550-650 F., on a bubble cap tray 53 at the bottom of a tower 54. The tower, provided with a protective lining of refractory material 56 below tray 53, may be operated at atmospheric pressure or above. The risers and overow weir on tray 53 are suciently high to form and maintain a relatively deep layer of sulfur, say about l5 to 24" deep, so that essentially all the reaction with air to form sulfur dioxide takes place therein. A valved line 55 enables sulfur to be drained from tray 53 as desired or required. The temperature of the liquid sulfur being oxidized is desirably controlled at below 700 F., preferably at about 550-650 F., by introducing to the pool liquid sulfur maintained at a temperature below auto-ignition level, preferably in the range of about 250 -3 10 F., at a predetermined rate, as through a spray nozzle S7 into free space above and contiguous to the pool at suitable distance above liquid level of the latter. Overflow liquid sulfur is continuously withdrawn from bubble cap tray 53 through line 58 and is pumped by means of pump 84 to a sulfur pit`59 where it may be cooled as described below.

In lieu of spray nozzle 57, liquid sulfur canbe pumped directly to tray 53 via an overow weir (not shown).

lt is preferred, however, to introduce the liquid sulfur through the spray nozzle, as shown, since by means thereof: (l) sulfur is distributed over bubble cap tray 53 at a uniform temperature with the result that tray temperature gradation is negligible, (2) presence of liquid sulfur in the space above tray 53 oiers protection against excessive temperatures caused byincomplete combustion on the tray itself, and (3) the spray system more eiectively cools the gases iiowing upwardly.

The product gases,resulting from the reaction of air with sulfur, having been cooled by contact with liquid sulfur introduced through spray nozzle 57, comprise sulfur dioxide containing reduced quantities of sulfur vapors and substantially free of elemental oxygen. The gases pass upwardly in tower 54 to bubble cap tray 5i where they are intimately contacted with liquid sulfur maintained at below auto-ignition level, preferably in the range of about 250 to about 310 F. The liquid sulfur is passed downwardly in countercurrent with the ow of gases at a su'icient rate to remove from the gases substantially all of the sulfur vapors entrained therein, and together therewith passes from tower 54 via conduit 62. From conduit 62 the liquid sulfur iiows to sulfur pit 59 lined with a protective refractory material 63 and dividend into two compartments, a cooling compartment 8i supplied with an agitator 64, and an overilow compartment 82. Water is injected through valved line 65 into cooling compartment 81, and cooling is accomplished by evaporation of the water. Resultant steam is released to the atmosphere through conduit 66. rthe cooled liquid sulfur is collected in overflow compartment S2 and may then be removed as sulfur product through valved line 67 or circulated by means of pump 68 through

lines

67 and 69 and valved line S3 to be passed downwardly through spray nozzle 57 countercurrent with the flow of generated sulfur dioxide.

A hydrogen suliide-containing gas may be introduced below bubble cap tray 61 through valved line 7l at which point it mixes with generated sulfur dioxide passing upwardly. Reaction between the sulfur dioxide and hydrogen sultide with formation of product gases containing sulfur vapors takes place at this point, the extent of the reaction being determined essentially by the concentration of the reactant gases, the length of residence of the reactant gases at such point and the temperature maintained therein. Liquid sulfur maintained at below auto-ignition temperature, preferably at a temperature ranging from about 25W-310 F., is pumped from overilow compartment 82 by means of pump 65 through

lines

67 and 69 and is introduced to the tower through valved line 72. rihe liquid sulfur passes downwardly through bubble cap tray 6i in countercurrent with the tiow of product gases at a suliicient rate to remove sulfur vapors from the product gases while cooling the gases by removing heat of reaction therefrom.

if desired or required, the hydrogen sulde containing gas may alternatively be introduced into the tower above bubble cap tray 6ft through valved line 73.

The resultant cooled gases pass upwardly in tower 54 through internal risers 7S within suitable catalyst 85 maintained at conditions favorable to the reaction ofl sulfur dioxide with hydrogen suliide to form elemental sulfur. The gases, thereby preheated to desired temperature, pass upwardly to plate 86 and are deflected downwardly through the catalyst. Beneath the catalyst there may be provided mist removal packing (not shown) which suitably may consist of coke or fibre glass. Such mist removal packing serves to entrap entrained sulfur that may be present as the result of the atomizing action of spray 57 or of bubble cap action on tray 61, as the case may be. Such packing, if used, minimizes sulfur deposit problems resulting from mechanical treatment or circulating liquid sulfur. In installations designed for a relatively coarse spray and relatively low gas velocities, the packing is not necessary.

Product gases resulting from the catalytic conversion and containing substantial quantities of sulfur vapors pass upwardly in tower 54 through external riser 87 and then through

bubble cap trays

74 and 75 where liquid sulfur introduced through valved conduit 72 passes downwardly Y in c't-.mntegr'current with the y rate te Aretrie-vje the Sartor-.vapors and together therewith Ypasses through 4pipe'r7'6 along bubble cap tray 61 and contain valuable constituents.

gnes-ss flow of gases at suicient sulfur. Wh'e'nrsu'ch 'a plurality of catalyst beds is provided, they aroused cooperation with additional sulfur con-V dense'r's or appropriate bubble cap trays to cool the reactant gases and remove elemental sulfur therefrom before they are introduced into the catalyst beds.

Y While VAin the description of Figures l and 2 we have referred to air as the means for obtaining oxidation of the liquid sulfur, any oxygen-containing gas maybe sub- Y j stituted therefor, as for example, commercial oxygen or oxygen-*enriched air.v 1

Itwill be 'understood that whileV we have described in detail certain speciieembodiments of our invention,

it is not our intention to have our invention limited to or circumscribed by the specic details of construction, arrangement of parts or procedure herein described and illustrated in view of the fact that our invention is susceptible ,to many modifications without departing from the scope of this disclosureV and the scope of the appended claims; i

The following examples represent typical operation of the sulfur dioxide generator'se'ction of Figure 2, terminating above Vspray nozzle 57;VY Y

Example 1.-Liquid sulfurat 290 F. was pumped from overow compartment 82 of sulfur pit 59 by means of pump 68'intoY spray nozzle 57-and onto bubble cap tray 53Vprovid`ed with risers and overflow weir to form a depth of-'22". Spray nozzle 57 was positioned 24" Vabove the liquid levelof the sulfur. The sulfur in the pit was maintained at 290 F. by surface water addition through valved line 653 A water tlow of about 1.6 gallons per Vminute was adequate to maintain the constant cooling pit temperature. When the circulation through bubble cap tray 53 was established, air was introduced through valved line 52 below ythe surface of the liquid sulfur, and the sulfur was ignited by an open llame Vrepresented by burner 79.. The burner was then turned olf, and the air and sulfur feed were adjusted until the temperature t of the liquid sulfur: on tray 53 rose to 640 F. while maintaining a constant overllow of sulfur through line 5S to cooling compartment S1 of sulfur pit 59. To attain Y the aforesaid temperature, the sulfur ow rate was approximately l2 gallons per minute, and the airrow rate was approximately k355 cubic feet per minute. The recirculation .'rate ofthe Vsulfur corresponded to about 3l times the rate of sulfur consumption. Generator tem-Y The product gases contained about 20.8% sulfur dioxide with approximately 0.2% oxygen on free sulfurfree basis. These gases at standard' conditions carried approximatelyr0-065 lb. of sulfur per cubic foot of gas,

Y such quantity of sulfur being about one-fth or less of the minimum sulfur content of product gases obtained when recirculation of liquid sulfur is not employed.

y Example`2.-'lfhe apparatus was brought u'p to requilibrium as described in Example l. The 'air and sulfur feed Ywere thenadjist'ed to maintain a generator operating t perature below 700 F. a stream of oxygen-containing Y temperature of o Il, 'To obtain such temperature, the

suiturnow' 'rate through the spray was approximately-6.91

gall-amper minute; the air new rate 'was approximately 16.0 cubic feet per' minute. The recirculation rate of .the sulfrcorresponded te about 48 'times the rate of sulfur consrnnption.V Average generator temperatures were as follows: Y Y y F. sulfurV 'to spray y 29o Sulfur on Vtray g `t 560YV Vapor above spray 540V The precinct gases estranea abetfzosU/'z sulfur dioxide-1 with approximately 0.2% oxygen on free sulfur-free basis. These 'gases at standard conditions carried approximately' dos in. c'fsnlfur per cubic footer gas:

The' following example represents.

sulde Vvto produce elemental sulfur,l In vthe specific apparatus 'employed,'bubble cap tray 75" was eliminated, and

Ycirculatingliquid sulfur was` introduced to the tower above bubble cap tray 74Y on the opposite Yside of the tower as illustrated. y Y l j YExample .i5-'Approximately 13.6 cubic feet per minute of Vair-' was'introduc'ed below generator tray 53 which con-l tained a pool of liquid sulfur 20 deep and maintained at G-65u" F. by passing cooled liquid Vsulfur through spray .3o. nozzle S7. The spray nozzle' was positioned 40 above the liquid level ofthe sulfur. The'resuitant gases containing'tabout 20.8 to 21.0% sulfur dioxide and about 0.2% oxygen onfree sulfur-free basis were mixedV with acid gas containing about v%v of hydrogen sulfide which was introduced 'at 6.4 cubic feet per minute through valved line 71.v The mixed gasesentei'ed'bubble'cap tray'61 where they were cooled to'280 ;300 F. by circulation of cooled t liquid sulfur from overflow compartment 82 of sulfur pit S? over the bubble cap At this point the sulfur con- 1 tent of the gases at standard conditions was about 0.0002 lb. per cubic Vfoot of gas. The gases were then preheated by indirect heatexchange and'i'nt-roduced to catalyst 85' at about 400 F., this temperature increasing within the Vcatalyst bed due to heat of reaction to about 800 F. 'at

the exit. Product sulfur resultingfrom the catalytic reaction of thehydrogen sulfide and sulfur dioxide was condensed on bubble cap tray 74 where it mixed with the circulated sulfur. The product sulfurrtogether with theV circulated sulfur was then removed from the system through lineg62, Residual gases were exhausted to the atmosphere. Overall conversion to elemental sulfur on the basis of'total acid gas introduced was labout 85%.

In theforegoing specification and in the appended claims, all references 'to auto-ignition temperature of sulfur areint'ended to include any temperature at which auto-ignition of'sulfur occurs, i. e. at about 500 F. or abVe; Y i i We claim:

l. A process for 'the production of elemental sulfur from hydrogen 'sulfide by reaction of a gaseous stream containing the Vsame With a gaseous stream containing,`

sulfu'rdioxide produced by combustion of sulfur which comprises: producing 'the second-named'gaseous stream substantially free of molecular oxygen and having low elemental 'sulfur content by (l) re'actingrto substantially complete consumption of its oxygen content withina pool of liquid sulfur maintained at auto-ignition temportion of the heet of combustion; ceeingthe Icemmstiz'm 'typical operation et the apparatus 'substantially as shown' Figure 2 andV in-k cludes reatio'n of generated sulfur dioxide with hydrogen products by direct contact of the same with a stream of circulating cooled liquid sulfur to condense from said combustion products substantially all of the sulfur vapors contained therein; reacting the rstand second-named gaseous streams under conditions to form a gaseous product containing elemental sulfur; cooling said gaseous product and extracting elemental sulfur therefrom by contact with a stream of circulating cooled liquid sulfur; and withdrawing as the sulfur product of the operation a portion or" the circulating cooled liquid sulfur.

2. A process according to claim l, wherein the cooled sulfur returned to the sulfur pool is introduced downwardly upon the top surface of the pool and in countercurrent contact with the combustion products leaving the pool.

3. A process for the production of elemental sulfur from hydrogen sulde by reaction of a gaseous stream containing the same with a gaseous stream containing sulfur dioxide produced by combustion ot sulfur which comprises: producing the second-named gaseous stream substantially free of molecular oxygen and having low elemental sulfur content by (l) reacting to substantially complete consumption or its oxygen content within a pool of liquid sulfur maintained at temperature of about SSW-650 E. a stream of air admitted to said pool (2) maintaining said pool at the aforesaid temperature by continuously withdrawing liquid sulfur from the pool, cooling the liquid Sulfur Withdrawn to temperature of about 250-310 F., returning the cooled sulfur to said pool, and effecting said withdrawal and return of sulfur at rate of about 25 to 60 times the rate of sulfur combustion to absorb substantially all of the heat of combustion; cooling the combustion products by direct contact of the same with a stream of circulating cooled liquid sulfur having a temperature of about 250-310 F. to condense from said combustion products substantially all of the sulfur vapors contained therein; reacting the irstand second-named gaseous streams under conditions to form a gaseous product containing elemental sulfur; cooling said gaseous product and extracting elemental sulfur therefrom by contact with a stream of circulating cooled liquid sulfur having a temperature of about 250-310 F.; and withdrawing as the sulfur product of the operation a portion of the circulating cooled liquid sulfur.

4. A process according to claim 3, wherein the streams of circulating liquid sulfur are combined after having performed their respective cooling duties and are cooled within a single cooling zone.

5. A process for the combustion of liquid sulfur to produce a stream of sulfur dioxide-containing gases substantially free of molecular oxygen and having lour elemental sulfur content which comprises reacting to substantially complete consumption of its oxygen content within a pool of liquid sulfur maintained at auto-ignition temperature below 700 F. a stream of oxygen-containing gas admitted to said pool, maintaining said pool temperature by continuously withdrawing liquid sulfur from the pool, cooling the liquid sulfur withdrawn to below auto-ignition temperature, returning the cooled liquid sulfur to said pool, and erecting said withdrawa and return of sulfur at rate in excess of about 25 times the rate of sulfur combustion to absorb at least a major portion of the heat of combustion.

6, A process for the combustion of liquid sulfur to produce a stream of sulfur dioxide-containing gases substantially free of molecular ox gen and elemental sulfur which comprises reacting to substantially complete consumption of its oxygen content within a pool of liquid sulfur maintained at temperature of about -550 F. a stream of air amnitted to said pool, maintaining said pool. temperature by continuously withdrawing liquid sulfur from the pool, cooling the liquid sulfur Withdrawn to a temperature of about 250-310 F., returning the cooled liquid sulfur to said pool, and eecting said withdrawal and return at rate of about 25 to 5G times the rate of sulfur combustion to absorb substantia ly all of the heat of combustion, and then cooling the resultant sulfur dioxide-containing gases by direct contact of the same with liquid sulfur having a temperature of about 25 310 F. to condense from said gases substantially all of the sulfur vapors contained therein.

References Cited in the file of this patent UNlTED STATES PATENTS

Claims

1. A PROCESS FOR THE PRODUCTION OF ELEMENTAL SULFUR FROM HYDROGEN SULFIDE BY REACTION OF A GASEOUS STREAM CONTAINING THE SAME WITH A GASEOUS STREAM CONTAINING SULFUR DIOXIDE PRODUCED BY COMBUSTION OF SULFUR WHICH COMPRISES: PRODUCING THE SECOND-NAMED GASEOUS STREAM SUBSTANTIALLY FREE OF MOLECULAR OXYGEN AND HAVING LOW ELEMENTAL SULFUR CONTENT BY (1) REACTING TO SUBSTANTIALLY COMPLETE CONSUMPTION OF ITS OXYGEN CONTENT WITHIN A POOL OF LIQUID SULFUR MAINTAINED AT AUTO-INGITION TEMPERATURE BELOW 700* F. A STREAM OF OXYGEN-CONTAINING GAS ADMITTED TO SAID POOL AND (2) MAINTAINING SAID POOL AT THE AFORESAID TEMPERATURE BY CONTINUOUSLY WITHDRAWING LIQUID SULFUR FROM THE POOL, COOLING THE LIQUID SULFUR WITHDRAWN TO BELOW AUTO-IGNITION TEMPERATURE, RETURNING THE COOLED SULFUR TO SAID POOL, AND EFFECTING SAID WITHDRAWAL AND RETURN OF SULFUR AT RATE IN EXCESS OF ABOUT 25 TIMES THE RATE OF SULFUR COMBUSTION TO ABSORB AT LEAST A MAJOR PORTION OF THE HEAT OF COMBUSTION; COOLING THE COMBUSTION PRODUCTS BY DIRECT CONTACT OF THE SAME WITH A STREAM OF CIRCULATING COOLED LIQUID SULFUR TO CONDENSE FROM SAID COMBUSTION PRODUCTS SUBSTANTIALLY ALL OF THE SULFUR VAPORS CONTAINED THEREIN; REACTING THE FIRST- AND SECOND-NAMED GASEOUS STREAMS UNDER CONDITIONS TO FORM A GASEOUS PRODUCT CONTAINING ELEMENTAL SULFUR; COOLING SAID GASEOUS PRODUCT AND EXTRACTING ELEMENTAL SULFUR THEREFROM BY CONTACT WITH A STREAM OF CIRCULATING COOLED LIQUID SULFUR; AND WITHDRAWING AS THE SULFUR PRODUCT OF THE OPERATION A PORTION OF THE CIRCULATING COOLED LIQUID SULFUR.